1. Field of the Invention
This invention relates generally to microwave transmission systems and in particular relates to a dual mode multiphase power divider.
2. Description of the Prior Art
In many microwave applications it is necessary to increase the transmitting power, reduce satellite intermodulation loss and provide beam shaping. One method of achieving the above objectives and also providing signal isolation is to channelize the transmitter frequency band into a number of smaller frequency bands. These channels are combined by a group of filters called a multiplexer. The performance of a multiplexer is improved when adequate guard bands exist between channels, but guard bands themselves represent unused bandwidth. When two multiplexers are used to combine the signals, alternate channels can be combined in each, so that the multiplexers become simple, efficient, and introduce a minimum of delay distortion. Two antennas, or two isolated ports of a single antenna must be provided a dual multiplexer transmitter. This invention deals with a new method of providing two isolated ports to a single antenna, each of which generates nearly the same beam pattern of the same polarization. A multiple antenna feed having a uniform phase progression is used, the sense of the phase progression is determined by which of the ports is excited. Such an arrangement was described in U.S. Pat. No. 3,680,143 which issued to J. S. Ajioka, et al. on July 25, 1972. With such antenna structures a shaped beam is realized by a plurality of linearly disposed offset feeds at the focal region of a reflector. The feeds are energized in a manner to produce different senses of phase progression across the aperture. The resulting patterns are sufficiently close so as to overlap. In an exemplary antenna having three feeds the relative phase progression across the adjacent horns in one mode might be +60.degree., 0.degree., and -60.degree., and in another mode -60.degree., 0.degree.,and +60.degree.. A power divider which has been used for providing such a phase progression is disclosed in U.S. Pat. No. 3,843,941 which issued to Thomas Hudspeth, et al. on Oct. 22, 1974. Such a power divider is realized by having 2 input ports feed into a cavity with a common conductive wall, several conductive septa and 3 output ports. This power divider is a rather complex device in a 3 output port configuration and a greater number of output ports may be extremely difficult to achieve utilizing the techniques of that patent.